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Arai Drum brake help

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Arai Drum brake help

Old 07-26-22, 03:30 PM
  #1  
Flipper71
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Arai Drum brake help

Hi all

There seems to be a lot of knowledge here, so I hope I'll be able to find a solution to my problem.

I have a Dawes tandem with an Arai drum brake. For all of my efforts I just cant get the wheel in the bike without the backing plate going out of adjustment. I have found various 'how-to' guides and have applied the brakes whilst tightening the lock-nut, but when I do the axle nuts up it causes the shoes to bind and scrape on the drum.

If any of that makes sense, I would be forever in your debt if someone has a workaround to stop this from happening.

I appreciate any help you may be able to provide.

Regards

Flipper71
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Old 07-26-22, 05:10 PM
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Rick
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I own a Tandem with an Arai drum brake. From how you describe the problem I am not understanding how to help you. Please send some pictures.
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Old 07-27-22, 05:12 AM
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Flipper71
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Originally Posted by Rick View Post
I own a Tandem with an Arai drum brake. From how you describe the problem I am not understanding how to help you. Please send some pictures.
Hi Rick, thank you for your reply. I'm not sure pics would help When I put the backing plate on there is a tiny gap around the hole, so after tightening the locknut (and applying the brake to centralize the shoes) the wheel spins freely, but after putting the wheel into the frames and tightening the wheel nuts it then starts to catch on the drum. Its almost like the backing plate is moving a minute amount, but just enough to cause the rubbing. It's to the point the wheel just doesn't spin freely. I have taken the wheel off about 10 times now and corrected it, but I just don't seem to be able to do anything with it to stop it from happening.
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Old 07-27-22, 08:46 AM
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Rick
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Flipper71: Please review this PDF and then describe the problem again.
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Old 07-27-22, 11:27 AM
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Originally Posted by Rick View Post
Flipper71: Please review this PDF and then describe the problem again.
+1 on this and pix.
A bunch of us here have experience with Arais, and pix always help.
Based on your description, I wonder if the hole isn't too big for your axle? (I believe I've read here that the housings came with differing hole sizes.) So maybe the stationary housing isn't resting up against the stationary hub axle when you tighten it, but pressing beyond and onto part of the hub that rotates (sorry for the inelegant terminology!)
But: pix.
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Old 07-27-22, 05:27 PM
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1. If you disconnect the brake cable while the wheel is installed does the drum still drag?
2. Is the backing plate rigidly held, or does it wobble around a bit when the wheel is installed?
3. Is the drag you are experiencing a light rub once per wheel revolution, or enough that the whee doesn’t want to spin freely?

Pictures always help.
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Old 07-28-22, 04:52 AM
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By your description it sounds like the brake shoe assembly (#2 in the pdf) is being displaced, or moved out of perpendicularity with the axle when the wheel is tightened in the dropouts. I would check both the drop outs to insure they are aligned as well as the axle is not bent
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Old 08-01-22, 11:19 PM
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Diagram 2, 12-15mm spacing.
It's not uncommon to lose the washer in the "guts" section of item number 8.
Your local hardware will have a suitable thick or thin washer. Installing the washer between the shoe plate & the inner axle nut will prevent the shoes & shoe plate from being smashed into the drum when the axle nut is tightened by physically moving the shoe plate outboard.
Per diagram 2, you have up to 15mm protrusion allowable & still be within specs. Surely, a 1 or 2mm washer could help, no?

Last edited by base2; 08-01-22 at 11:29 PM.
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Old 08-04-22, 08:46 AM
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By your description you need a bushing to take up the small difference in diameter of the axle. Washers will not work to center the axle because the braking force on the hub will push the hub off center. They will help to secure the wheel...
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Old 08-04-22, 09:12 AM
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Originally Posted by xlbs View Post
By your description you need a bushing to take up the small difference in diameter of the axle. Washers will not work to center the axle because the braking force on the hub will push the hub off center. They will help to secure the wheel...
The axle centers in the drop outs.

The hole in the shoe plate allows the shoe plate to center to the drum.

The shoe plate is centered to the drum by using your forefinger & thumb to squeeze the brake lever arm towards the reaction arm thereby causing to brake pads to move outward towards the drum & move the plate to the actual "in-use" center.

When it is in the actual "in-use" center, apply the jam nut to the axle secure the shoe plate in place.

Release your thumb & forefinger & install the wheel.

The slight play between the axle nub & hole in the shoe plate is necessary so that both shoes apply to the drum equally & concentrically.

Last edited by base2; 08-04-22 at 09:15 AM.
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Old 09-06-22, 09:27 AM
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Arai offered the "backing plate" with different diameter center-bore holes to fit different axle diameters. I believe they offered 14mm to fit Edco/Hadley hubs and 10mm for others (like Shimano). From your description it sounds like your plate has a larger hole than the diameter of your axle, causing the plate to shift enough that the pads rub. Short of getting a plate with the correct size bore, not sure how you could remedy this without some custom machining or something. Precision Tandems suggests that you could weld up the hole and redrill it to the smaller size, but that would take some serious precision work as the hole has to be perfectly redrilled or else you're back to the same issues. https://www.precisiontandems.com/arai.htm
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Old 09-06-22, 11:22 PM
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Originally Posted by Philly Tandem View Post
Arai offered the "backing plate" with different diameter center-bore holes to fit different axle diameters. I believe they offered 14mm to fit Edco/Hadley hubs and 10mm for others (like Shimano). From your description it sounds like your plate has a larger hole than the diameter of your axle, causing the plate to shift enough that the pads rub. Short of getting a plate with the correct size bore, not sure how you could remedy this without some custom machining or something. Precision Tandems suggests that you could weld up the hole and redrill it to the smaller size, but that would take some serious precision work as the hole has to be perfectly redrilled or else you're back to the same issues. https://www.precisiontandems.com/arai.htm
In the world of machining, the hole doesn't need to be terribly accurate. I had good luck welding on a stock washer. I did machine off some material first, but a motivated individual with a file could do the same without the mill. I have a suspicion one could find a press in bushing of a close enough size and achieve success.
Unexpected spacer behind Arai drum
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